The present invention relates to a tire inflation pressure monitor that informs a driver in a vehicle of the tire inflation pressure and the monitoring method.
A wireless tire inflation pressure monitor that notifies a driver of a vehicle of the tire inflation pressures is known. As shown in FIG. 8, a typical tire inflation pressure monitor 51 includes four transmitters 53 and a receiver 54. The transmitters 53 are respectively located in tires 52 and the receiver 54 is located in the body of the vehicle 50.
Each transmitter 53 measures the internal air pressure of the corresponding tire 52. Each transmitter also modulates signals to reflect data concerning the measured tire inflation pressure and transmits the signals from transmission antennas (not shown) by radio waves.
As shown in FIG. 7 and 8, the receiver 54 includes four reception antennas 56, which respectively correspond to the four transmitters 53. The receiver 54 also includes a reception circuit 57 and a controller 58. A display 55 is located in the passenger""s compartment and is connected to the receiver 54.
The reception circuit 57 receives radio waves from the transmitters 53 through the reception antennas 56. The reception circuit 57 demodulates the radio waves, which reveals the pressure data, and sends the data to the controller 58. The controller 58 commands a display 55 to display information concerning tire inflation pressure based on the input data.
The reception antennas 56 induce voltage in accordance with the electric field intensity of the radio waves from the transmitters 53. When the voltage induced by the reception antennas 56 is greater than a predetermined value, the reception circuit 57 detects the induced voltage and processes the voltage signal to produce the necessary data. When the voltage induced by the reception antennas 56 is smaller than the predetermined value, the reception circuit 57 does not detect the induced voltage. In this way, if the voltage induced by the reception antennas 56 is not high enough to be detected by the reception circuit 57, the receiver 54 cannot receive data from the transmitters 53.
Since the transmitters 53 are installed in the tires 2, the position of each transmitter relative to the reception antenna 56 of the receiver 54 continuously varies when the vehicle 50 is running. The transmission antennas of the transmitters 53 and the reception antenna 56 of the receiver 54 each have directivity. Therefore, the electric field intensity of radio waves from the transmission antennas received at each reception antenna 56 continuously varies when the vehicle 5 is running. In other words, the voltage induced at each reception antenna 56 continuously varies and the reception circuit 57 may not detect the induced voltage. Therefore, the signal reception of the prior art receiver 54 is not stable.
An objective of the present invention is to provide a tire inflation pressure monitor and a monitoring method that produce stable signal reception.
To achieve the above objective, the present invention provides a receiver for receiving radio waves that carry data representing a physical state. The radio waves are transmitted by a transmitter. The receiver includes a plurality of reception antennas that respectively induce voltage signals based on reception of the radio waves, a synthesizer for synthesizing the induced voltage signals into one voltage signal, and a processing device for processing the synthesized voltage signal to obtain the data.
The present invention also provides a tire inflation pressure monitor having a transmitter located in a vehicle tire for transmitting data concerning the inflation pressure of the tire by radio waves and a receiver for receiving the data from the transmitter. The receiver includes a plurality of reception antennas that respectively induce voltage signals based on reception of the radio waves, a synthesizer for synthesizing the induced voltage signals into a synthesized voltage signal, and a processing device for processing the synthesized voltage signal to obtain the data.
The present invention further provides a method including: transmitting data representing a physical state by radio waves; receiving the radio waves and inducing voltage signals with reception antennas, respectively; synthesizing the induced voltage signals into one voltage signal; and processing the synthesized voltage signal to obtain the data.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.